Ablation catheters using RF (radio frequency) energy are known. A typical ablation catheter has electrodes located at the catheter tip and delivers RF energy to ablate selected tissue areas in a patient. For example, patients with arrhythmia experience irregular heart beats caused by arrhythmogenic electrical signals generated in cardiac tissues. Such patients may be treated by ablating those cardiac tissues that generate such unintended electrical signals with RE energy. With the help of sensing and mapping tools, an electrophysiologist can determine the region of cardiac tissue targeted for ablation. Once determined, a catheter tip having one or more electrodes is positioned over the targeted tissue. Then, the user sends RF energy from the generator to the electrodes, creating sufficient heat to damage the targeted tissue. By damaging and scarring the targeted tissue, aberrant electrical signal generation or transmission is interrupted.
Application of curative energy is currently performed endocardially with the objective of reaching the epicardium to create a fully transmural. This is important in all arrhythmias especially during ablation for atrial fibrillation and ventricular tachycardia. In the former case, transmural lesions are required to create conduction block to isolate relevant structures while in the latter case the arrhythmogenic substrate is located often in the epicardial layer of ventricular walls. Delivery of the energy is limited by the increase of temperature at the interface between catheter tip and endocardial surface and there is a good correlation between thrombus formation and high temperature. A temperature sensor is typically provided near the tip of the catheter so the user may monitor the operating temperature to ensure that overheating does not occur in the catheter tip and in the surrounding tissues. One known solution to prevent overheating is by having an irrigation system embedded within the catheter. In brief a typical irrigation system includes a delivery lumen inside of the catheter body to supply cooling fluid, such a saline, from a pump to the catheter tip. An irrigation system may internally irrigate the catheter tip, where the cooling fluid circulates within the catheter tip. Another type of irrigation system delivers cooling fluid from within the catheter tip to the outside of the catheter tip which also cools the surrounding tissues. Catheters with an irrigated tip allow the delivery of more energy with a lower temperature at the tissue/catheter interface thus minimizing thrombus formation while maximizing deep lesion creation in the tissue. Despite numerous desirable properties, however, known irrigated catheters have several disadvantages. For example, because the temperature of the catheter tip region can vary depending on factors such as its proximity to an electrode and irrigation duct, it is difficult to monitor and ensure that all heated surfaces along the catheter tip are adequately cooled. Often the catheter tip is positioned not perpendicularly to the tissue but tangentially to increase the tip/tissue contact area as for example during ablation of the inferior part of the right sided pulmonary vein. In this situation and in every other situation where a tip side/tissue contact is required, a uniform cooling of the catheter tip would further reduce thrombus formation while allowing development of larger electrodes to more efficiently deliver energy for ablation. In this way the entire electrode surface can be used to ablate a pathological tissue without overheating any portion of the catheter tip and causing thrombus formation.
The coronary sinus (CS) is increasingly recognized as one of the major structures contributing in many types of supraventricular tachycardias including atrial fibrillation. In this case many anatomical and electrophysiological features can promote atrial fibrillation maintenance, especially in patients with a long-standing arrhythmia. As a matter of fact, the CS connects anatomically and electrophysiologically the right atrium and the left atrium with special characteristics of slow and anisotropic conduction, allowing micro- and macro-reentry during organized and unorganized atrial fibrillation. On the right atrial side, broad and thick muscular connections can be observed at the CS ostium, while different anatomic studies have demonstrated the existence of discrete and multiple connections (average 5±23 between the CS body and the LA postero-inferior and postero-lateral walls. This muscular extension of the left atrial wall into the CS shows marked anisotropy, and mapping their insertion with conventional bipolar and quadripolar catheters is relatively difficult given also the oblique insertion of these sleeves across the posterior pericardial space.
The role of the CS is increasingly recognized in maintaining persistent and permanent atrial fibrillation which constitute up to 70% of the atrial fibrillation cases in the population referred for catheter ablation. On one side during ablation of long-standing atrial fibrillation, disconnection of the coronary sinus from both the left and right atrium can be required in up to 60% of cases to interrupt the arrhythmia or to organize the electrical activity in a discrete mappable atrial tachycardia. On the other side, mitral isthmus ablation to create a bi-directional line of block is increasingly performed to organize the substrate during chronic atrial fibrillation ablation. To create a bi-directional block, ablation within the CS has to be performed in 30-50% of cases. The role of CS as a critical part of left atrial tachycardia is also increasingly known. Effective mitral isthmus block in the settings of perimitral atrial flutter can require ablation in the CS in up to 50% of cases to interrupt the arrhythmia and make it no longer inducible. The CS is also important in the ablation of postero-septal and left-sided accessory pathways, as in many cases the ventricular and/or atrial insertion of the accessory pathway is too epicardial for endocardial ablation using a conventional catheter. Furthermore mapping the CS body with a conventional multi-polar catheter is not quite efficient since this type of catheter is not able to deliver radio-frequency energy.
Thus, there remains a need for a balloon or a mesh expandable catheter that could be inserted deeply inside the CS, inflated and then slowly pulled back towards the CS ostium while delivering equatorially curative energy source such as radiofrequency or therapeutic ultrasound to fully disconnect the CS musculature from the left and right atrium in atrial fibrillation, atrial tachycardia or WPW ablation. It would be more beneficial clinically if this balloon catheter consists of multiple ablating irrigated electrodes where the irrigation pattern is controlled to provide desired relative uniform cooling to the ablating electrodes to minimize coagulum formation and create larger and longer lesions safely.